The 2251, Pannier, N class, WD, all have the same motor configuration, and installation is similar in most cases. The small board containing the capacitor should be discarded and the decoder soldered to the pickup wires (Red & Black) and the motor (Orange and Grey) In the case of the 2251 the micro decoder (DZ121/143) will fit between the middle wheel splashers, mine normally get a coat of paint to disguise them. The N Class, Pannier, and WD the decoder fits on top of the motor its protected by the metal plate that used to hold the board. In most cases wire need to be removed from the decoder harness as space is restricted. All these loco’s have superior running, thanks to the reliable Buhler can motor.